The Aunt Mall Cop being a Cultist theory is fairly strong. Why doesn't she appear during the last day...? Along with the constant vague threats, but that one's the strongest.
Yeah, that was my thoughts as I was thinking back over the ending. She’s not in the epilogue, she seems at best annoyed and at worst a little threatening towards Mae on some occasions, and she was right nearby when the gang found the severed arm. And at least motive-wise, if she heard anything at all from Mae’s mom and dad about their money/house troubles because of Mae’s illness, that might serve as a motivation for the harsh attitude towards her…basically blaming her for her parents’ stress.
BUT on the other hand, there could be completely other explanations for all of that, too. The power of ambiguity~!
And with regards to Eide/the cultist that attacked Mae, we can see that it’s a cat silhouette, so that could be any number of possibilities…Aunt Molly, or Grandad, or Casey, or that calico cat who lost his job (not remembering his name now), or just a random townsperson that has no strong relation to anyone. I just think Aunt Molly is one of the more likely candidates. Although one thing throwing me off is that the silhouette has a notched ear, like Mae, and Aunt Molly doesn’t have notched ears, at least last we saw her.